1SYSTEMD.TIMER(5) systemd.timer SYSTEMD.TIMER(5)
2
6 systemd.timer - Timer unit configuration
7
9 timer.timer
10
12 A unit configuration file whose name ends in ".timer" encodes
13 information about a timer controlled and supervised by systemd, for
14 timer-based activation.
15 This man page lists the configuration options specific to this unit
17 type. See systemd.unit(5) for the common options of all unit
18 configuration files. The common configuration items are configured in
19 the generic [Unit] and [Install] sections. The timer specific
20 configuration options are configured in the [Timer] section.
21 For each timer file, a matching unit file must exist, describing the
23 unit to activate when the timer elapses. By default, a service by the
24 same name as the timer (except for the suffix) is activated. Example: a
25 timer file foo.timer activates a matching service foo.service. The unit
26 to activate may be controlled by Unit= (see below).
27 Note that in case the unit to activate is already active at the time
29 the timer elapses it is not restarted, but simply left running. There
30 is no concept of spawning new service instances in this case. Due to
31 this, services with RemainAfterExit= set (which stay around
32 continuously even after the service's main process exited) are usually
33 not suitable for activation via repetitive timers, as they will only be
34 activated once, and then stay around forever.
35
37 Implicit Dependencies
38 The following dependencies are implicitly added:
39 · Timer units automatically gain a Before= dependency on the service
41 they are supposed to activate.
42 Default Dependencies
44 The following dependencies are added unless DefaultDependencies=no is
45 set:
46 · Timer units will automatically have dependencies of type Requires=
48 and After= on sysinit.target, a dependency of type Before= on
49 timers.target, as well as Conflicts= and Before= on shutdown.target
50 to ensure that they are stopped cleanly prior to system shutdown.
51 Only timer units involved with early boot or late system shutdown
52 should disable the DefaultDependencies= option.
53 · Timer units with at least one OnCalendar= directive will have an
55 additional After= dependency on time-sync.target to avoid being
56 started before the system clock has been correctly set.
57
59 Timer files must include a [Timer] section, which carries information
60 about the timer it defines. The options specific to the [Timer] section
61 of timer units are the following:
62 OnActiveSec=, OnBootSec=, OnStartupSec=, OnUnitActiveSec=,
64 OnUnitInactiveSec=
65 Defines monotonic timers relative to different starting points:
66 OnActiveSec= defines a timer relative to the moment the timer
67 itself is activated. OnBootSec= defines a timer relative to when
68 the machine was booted up. OnStartupSec= defines a timer relative
69 to when systemd was first started. OnUnitActiveSec= defines a
70 timer relative to when the unit the timer is activating was last
71 activated. OnUnitInactiveSec= defines a timer relative to when the
72 unit the timer is activating was last deactivated.
73 Multiple directives may be combined of the same and of different
75 types. For example, by combining OnBootSec= and OnUnitActiveSec=,
76 it is possible to define a timer that elapses in regular intervals
77 and activates a specific service each time.
78 The arguments to the directives are time spans configured in
80 seconds. Example: "OnBootSec=50" means 50s after boot-up. The
81 argument may also include time units. Example: "OnBootSec=5h 30min"
82 means 5 hours and 30 minutes after boot-up. For details about the
83 syntax of time spans, see systemd.time(7).
84 If a timer configured with OnBootSec= or OnStartupSec= is already
86 in the past when the timer unit is activated, it will immediately
87 elapse and the configured unit is started. This is not the case for
88 timers defined in the other directives.
89 These are monotonic timers, independent of wall-clock time and
91 timezones. If the computer is temporarily suspended, the monotonic
92 clock stops too.
93 If the empty string is assigned to any of these options, the list
95 of timers is reset, and all prior assignments will have no effect.
96 Note that timers do not necessarily expire at the precise time
98 configured with these settings, as they are subject to the
99 AccuracySec= setting below.
100 OnCalendar=
102 Defines realtime (i.e. wallclock) timers with calendar event
103 expressions. See systemd.time(7) for more information on the syntax
104 of calendar event expressions. Otherwise, the semantics are similar
105 to OnActiveSec= and related settings.
106 Note that timers do not necessarily expire at the precise time
108 configured with this setting, as it is subject to the AccuracySec=
109 setting below.
110 May be specified more than once.
112 AccuracySec=
114 Specify the accuracy the timer shall elapse with. Defaults to 1min.
115 The timer is scheduled to elapse within a time window starting with
116 the time specified in OnCalendar=, OnActiveSec=, OnBootSec=,
117 OnStartupSec=, OnUnitActiveSec= or OnUnitInactiveSec= and ending
118 the time configured with AccuracySec= later. Within this time
119 window, the expiry time will be placed at a host-specific,
120 randomized, but stable position that is synchronized between all
121 local timer units. This is done in order to optimize power
122 consumption to suppress unnecessary CPU wake-ups. To get best
123 accuracy, set this option to 1us. Note that the timer is still
124 subject to the timer slack configured via systemd-system.conf(5)'s
125 TimerSlackNSec= setting. See prctl(2) for details. To optimize
126 power consumption, make sure to set this value as high as possible
127 and as low as necessary.
128 RandomizedDelaySec=
130 Delay the timer by a randomly selected, evenly distributed amount
131 of time between 0 and the specified time value. Defaults to 0,
132 indicating that no randomized delay shall be applied. Each timer
133 unit will determine this delay randomly before each iteration, and
134 the delay will simply be added on top of the next determined
135 elapsing time. This is useful to stretch dispatching of similarly
136 configured timer events over a certain amount time, to avoid that
137 they all fire at the same time, possibly resulting in resource
138 congestion. Note the relation to AccuracySec= above: the latter
139 allows the service manager to coalesce timer events within a
140 specified time range in order to minimize wakeups, the former does
141 the opposite: it stretches timer events over a time range, to make
142 it unlikely that they fire simultaneously. If RandomizedDelaySec=
143 and AccuracySec= are used in conjunction, first the randomized
144 delay is added, and then the result is possibly further shifted to
145 coalesce it with other timer events happening on the system. As
146 mentioned above AccuracySec= defaults to 1min and
147 RandomizedDelaySec= to 0, thus encouraging coalescing of timer
148 events. In order to optimally stretch timer events over a certain
149 range of time, make sure to set RandomizedDelaySec= to a higher
150 value, and AccuracySec=1us.
151 Unit=
153 The unit to activate when this timer elapses. The argument is a
154 unit name, whose suffix is not ".timer". If not specified, this
155 value defaults to a service that has the same name as the timer
156 unit, except for the suffix. (See above.) It is recommended that
157 the unit name that is activated and the unit name of the timer unit
158 are named identically, except for the suffix.
159 Persistent=
161 Takes a boolean argument. If true, the time when the service unit
162 was last triggered is stored on disk. When the timer is activated,
163 the service unit is triggered immediately if it would have been
164 triggered at least once during the time when the timer was
165 inactive. This is useful to catch up on missed runs of the service
166 when the machine was off. Note that this setting only has an effect
167 on timers configured with OnCalendar=. Defaults to false.
168 WakeSystem=
170 Takes a boolean argument. If true, an elapsing timer will cause the
171 system to resume from suspend, should it be suspended and if the
172 system supports this. Note that this option will only make sure the
173 system resumes on the appropriate times, it will not take care of
174 suspending it again after any work that is to be done is finished.
175 Defaults to false.
176 RemainAfterElapse=
178 Takes a boolean argument. If true, an elapsed timer will stay
179 loaded, and its state remains queriable. If false, an elapsed timer
180 unit that cannot elapse anymore is unloaded. Turning this off is
181 particularly useful for transient timer units that shall disappear
182 after they first elapse. Note that this setting has an effect on
183 repeatedly starting a timer unit that only elapses once: if
184 RemainAfterElapse= is on, it will not be started again, and is
185 guaranteed to elapse only once. However, if RemainAfterElapse= is
186 off, it might be started again if it is already elapsed, and thus
187 be triggered multiple times. Defaults to yes.
188
190 systemd(1), systemctl(1), systemd.unit(5), systemd.service(5),
191 systemd.time(7), systemd.directives(7), systemd-system.conf(5),
192 prctl(2)
193systemd 241 SYSTEMD.TIMER(5)